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Saturday, 8 September 2012

What is Gravity and why does it work?

Since
Issac Newton, scientists have tried to grasp one of the 4 fundamental forces of
nature. Gravity. The weaker of the 4 forces but yet little is known about the
way it operates. We understand how it has a relationship with mass/matter and
that gravity due to relativity can alter or bend space and time if strong enough.
Examples of this would be black holes. Infinitely massive particles but reduced
to an infinitely small space. Such compression typically makes a black hole.
Though as mentioned in my previous posts black holes are not portals to another
world or plane of existence. But what is inside them, is a tiny dot with so
much mass, and light is unable to escape the clutches of the void.

So
what is gravity, in its purest sense? How does it work? Well there are two
answers to this question:

1)
Nobody knows. It just does.

2)
There's a very peculiar property of gravity that people have noticed for a long
time. In particular, "gravitational charge" is exactly the same
quantity as "inertial mass". That is, the "m" in the
formula "F = G m1 m2 / r2" for gravitational attraction is exactly
the same stuff as in the formula "F = ma". That is interesting,
because there's no particular reason why that should be the case. But, for
everything we've been able to measure (to exquisite accuracy) the "m"
in the first formula is exactly the same as the "m" in the second
formula, so that everything accelerates the same in the same gravitational
field.

Well,
forces with that property are often called "pseudo forces" and when they
are observed they're usually just symptoms that you chose the wrong coordinate
system to consider your problem. "Centrifugal force" is an example of
a force like that -- if you're inside a sealed centrifuge, you can immediately
tell that you are, even if you can't see out, because you stick to the walls.
But someone in a near-inertial frame sitting around the outside of the
centrifuge can see that the walls of the centrifuge are really just pulling you
inward with an acceleration a, and f_centrifugal = m_you * a_centrifuge.
(f=ma).

Fig.1 Matter interacting with Gravity, and is influencing the space time fabric

Credit: PhysicsForum.com

The
cool thing about Einstein's general theory of relativity is that it does away
with the coincidence between the two kinds of mass. He instead explained
gravity as a curvature of space time itself so that the straightest possible
path through space and time curves slightly in the vicinity of mass. To do
that, he had to produce a unified theory of space and time, which has us living
in a four-dimensional place called "space time". The time axis is
special in some ways but just like the spatial axes in other ways, for many
things, you can treat time as "just" a different direction than the
three we're used to.

The
curvature is usually very, very slight, one of the important things to
realize about Einsteinian relativity is that everything in the Universe is
zipping along the "time" axis at the speed of light -- so if it takes
you one second to jump up 4 feet from the ground and fall back down onto it,
the amount of curvature of your trajectory is spread out over a complete
light-second of motion (30,000 kilometres along your time axis). But because we
don't perceive motion on the time axis directly, that curvature is very, very
foreshortened and your trajectory looks like a tight parabola, just like you
can spot a very slight bend in a pool cue by sighting down the length of the
cue to foreshorten the cue itself.

Fig.2 Matter getting sucked in by a sheer gravitational vortices

Now, why does mass bend space time? Nobody knows. There are some very good ideas
floating around, but the only solid answer right now is that nobody has been able
to figure out why it actually happens. Though the unification of Quantum
gravity is the makeup of General Relativity and Quantum Mechanics, which
recently has taken a hit in the world of theoretical physics from analysed
Gamma Ray Bursts. But in principle, no one theory has been proposed and has
been proven, leading to an ever changing battle for the Grand Unified Theory.

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Since this is not a personal blog, I will disclose very little about myself. I enjoy science and wish to make this site a vessel for scientific knowledge. I will not post up personal information of any sorts about myself (Facebook, Address Book etc.). Enjoy the journey.